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PERMIAN, TRIASSIC, AND JURASSIC BEDDED RADIOLARIAN
CHERTS IN NORTH PALAWAN BLOCK, PHILIPPINES:
EVIDENCE OF LATE MESOZOIC SUBDUCTION-ACCRETION

Yukio lsozaki, Editha A. Amiscaray,
and
Aristotle Rillon

 

 

 

INTRODUCTION



Recent workers believe that the Cenozoic tectonic evolution of the Phillippine Archipelago involves the tectonic interactions of the Philippine Sea, Luzon Arc, South China Sea and subordinate older arcs (Hamilton, 1979; Holloway; 1982; Mc Cabe et al., 1982). The incipient ermplacement of the pre-Tertiary rocks on these islands predates the opening of the South China Sea during 32-17 Ma, mid-Oligocene to Early Miocene (Taylor and Hayes, 1980). This phenomenon partly connotes Late Mesozoic tectonic evolution of the eastern continental margin of Asia prior to the subsequerrt attenuation and fragmentation of continental crust along with the opening ofthe South China Sea (Hamilton; Holloway), However; little is known on the pre-Cenozoic tectonics of the region owing to scarce information on pre-Tertiary stratigraphy, geologic structures and fossil controls.

In the Philippines, pre-Tertiary rocks are confined mostly to ht soouthwestern portion  of the Archipelago, in the so-called North Palawan Block of Hashimoto and Sato, 1973 and Balce, 1976. The region is characterized by the presence of Paleozoic and Mesozoic sediments and metamorphics; Cenozoic and Cretaceous rocks and make-up the rest of the Archipelago.

This paper deals with the bedded radiolarian cherts of the North Palawan Block (Fig. 1). The chert is considered to be Middle-Late Permian. Early Jurassic and Late Jurassic bedded cherts in addition to the Middle Triassic ones. The finding of the Late Jurassic chert  necessitates revision in the tectono-sedimentary history of the North Palawan Block.

This study was undertaken as an activity of the pre- Tertiary project of the Paleontology and Stratigraphy Section, Geological Survey Division of the Philippine Bureau of Mines and Geo-Sciences. Fieldwork was conducted in March 1987 by the junior writers. Micropaleontological analysis was done by the senior writers in Yaamaguchi University.

 

 

 

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